Weakness in malignancy: evidence for a remote effect of tumor on distal axons.

Malignant tumors are known to have a "remote" or nonmetastatic effect on the central and peripheral nervous systems. Eight patients were seen with proximal muscle weakness in association with bronchogenic carcinoma (5), carcinoma of breast (2), and leukemia (1). Electromyography demonstrated small polyphasic motor unit potentials. Muscle biopsy, however, showed evidence of denervation. Electron microscopy revealed morphological abnormalities in the intramuscular segments of axons. This combination of EMG and biopsy findings is presented as evidence for a remote effect of tumor on the intramuscular distal axons.